It took over a hundred years to get from the first practical optical rifle scope (1844) to the first rifles without iron sights (1958). Now, iron sights are the exception – scopes rule.
Why Use a Rifle Scope?
A rifle scope is intended to facilitate long-range shooting by making it easier to see the target (and whatever is behind it), even when there is very little light.
Using a scope, shooters can take accurate shots in conditions whether they would have been working, literally, blind, in the days before scopes. This in turn enables them to benefit from other advances in long-range shooting technology, such as modern rifles which can shoot both farther and faster than their historic counterparts.
Why Your Rifle Scope Matters More Than Your Rifle
Many experienced shooters will tell you that they will happily spend more on their scope than they will on their rifle and this is a perfectly serious comment. The whole point of using a rifle is to hit the target for which you are aiming. Missing that target is frustrating. Hitting a target you did not intend to hit can be, literally, deadly.
Your scope, if you choose it wisely, is what will allow you to see what you are doing so you can use your rifle both enjoyably and safely. This means that you should buy the absolute best scope you can possibly afford, even if it means reducing the budget for your rifle itself.
With that in mind, here is a guide to rifle scopes to tell you everything you need to know to choose the best scope for your shooting level and intended use.
An Overview of a Rifle Scope
From the outside, a rifle scope is essentially a metal tube with some knobs around the middle and a lens at each end.
Modern tubes are usually made from aircraft-grade aluminum, which is why they are so much lighter than older tubes, which were made of steel. They are also available in a variety of finishes, most of which are essentially variations on matte and gloss. If you’re hunting, a dark, matte finish is your only option as anything shiny will warn animals for miles around.
The knobs in the middle of the tube are to make various adjustments to allow the scope to function more accurately. If you are using a rifle scope with an adjustable level of magnification, there will also be a magnification ring somewhere within easy reach.
The lens which goes up by your eye is known as the ocular lens and its opposite number is known as the objective lens. They are housed in “bells” and the bell for the ocular lens should have a locking ring on it (if it’s good quality). There are more lenses inside the scope, usually around six.
Last but definitely not least, there is the reticle, commonly known as the cross-hairs. This is actually located inside the rifle scope, but, obviously, it is (or should be) clearly visible through the ocular lens.
Rifle Scopes Explained
Here is a closer look at each of the key parts of a rifle scope and what they mean for its functionality.
In the U.S. most tubes are 1″ in diameter, however, some scopes now use the European standard of 30mm (1.18″). This slight increase in diameter makes for a larger cross-sectional area. The benefits of this are more strength and rigidity plus the physical space to support a wider range of adjustments. The drawback, however, is that it increases the weight and bulk of the rifle scope.
Most tubes will have either three or four knobs for different sorts of adjustments. Ideally, you want these knobs to be easy to work, even with gloves on (or cold hands) and to give good feedback (a nice click or “thunk”) when you change the step. In the old days, the adjustment knobs would typically have caps on them, but these days that’s less common.
The three knobs you are almost guaranteed to find are windage, elevation, and focus and the fourth is parallax. Parallax adjustment is really only for long-range scopes, but the average modern rifle scope will probably have it.
Windage and Elevation
Windage is horizontal adjustment and elevation is vertical adjustment. Both forms of adjustment are measured in either minutes of angle or milliradians. Technically, both of these measurements relate to variances on a target at 100 yards. For practical purposes, all you really need to know is that one minute of angle (MOA) equals 1.047″ and one milliradian (MIL) equals 3.599″.
So, for example, if a rifle scope is advertised as having adjustment of 1/4 MOA then it means that each stage of the adjustment knob will move the bullet’s point of impact (PoI) by 1/4″. If it’s advertised as having 0.1 MIL then each click will move the PoI by 1/3″ (both at 100 yards).
For completeness, it has to be acknowledged that windage and elevation adjustments are a notorious weak spot even on premium scopes. Most experienced shooters will tend to take the stated adjustments with at least a pinch of salt.
That said, it’s also fair to say that these adjustments rely on moving parts that are quite fragile and hence benefit from gentle treatment. There isn’t likely to be a whole lot you can do about recoil, but try to avoid dropping your scope and if you travel with it, then treat it to some decent protection, especially if you are traveling by air and putting it in your cargo luggage. Remember, baggage handlers are not renowned for treating items gently no matter how many warnings you put on them.
Focus basically allows a shooter to customize the reticle to their particular eye. All you do is point the scope at something big and blank like a wall (or the sky, or grass) and turn the ocular-lens bell until the reticle is in sharp focus. Then lock it into place.
For practical purposes, parallax means distance. Some scopes will be set at the factory but most will be adjusted manually to allow for more flexibility in use. Your options for parallax adjustment are either a knob on the turret or a calibrated objective lens bell. These days, it’s usually the former. In either case, you’ll need to remember to do it otherwise your scope will mislead you as to the location of your target and you’ll aim at the wrong place. This is known as parallax error.
The Magnification Ring and Eye Relief
The magnification ring does exactly what its name suggests, it adjusts the level of magnification (or power) on your scope. As it does so, the length of the scope will change and this will influence the level of eye relief.
Eye relief is the distance between the shooter’s eye and the ocular bell. It’s called eye relief because it’s what relieves your eyes of the pain of being hit by an aluminum tube as your rifle kicks. It, therefore, relieves you of the inconvenience and expense of making regular trips to the hospital for stitches.
When it comes to eye relief, the generally-accepted rule is that more is better. This does, however, have to be balanced by practicality. With that in mind 3″ is really the absolute minimum you should accept for a standard rifle. Many scopes now have 3.5″ some even have 4″.
For clarity, you need to look at the level of eye relief available when the scope is at its maximum extension.
It’s impossible to overstate the importance of the lenses in a rifle scope. It’s also impossible to overstate the importance of understanding that numbers, while important, only tell part of the story. The quality of the lenses is what really matters.
First of all, you want a high-quality glass. Ideally, you want ED glass, which is extra-low-dispersion glass, which offers the sharpest images and truest colors. This is sometimes marketed as HD glass, presumably to capitalize on the recognition of HD TVs, but it’s actually completely different. The glass needs to be ground to shape effectively and appropriately coated.
Coatings improve light transmission by reducing glare and reflection. They can also protect against water and scratches.
As a minimum, there should be a single layer of coating on one surface and it’s preferable if there’s at least a single layer on all surfaces. Better-quality scopes will typically have multiple layers on at least one surface and the very best will have multiple layers on all surfaces.
For completeness, if you anticipate doing a lot of shooting in damp conditions (which can include humidity, mist, and fog as well as rain), then look out for hydrophilic and hydrophobic coatings which disperse water quickly. The best of these will allow you to shoot accurately in even pouring rain.
Objective Lens Diameter
When reading the description of a scope, the number quoted after the power is the objective lens diameter. This is always quoted in millimeters. So “3.5-10×50” means the objective lens diameter is 50mm and “4×32” means it is 32mm.
As the size of an objective lens goes up, so does its field of view and so does its ability to let in light and hence its performance in low-light conditions. The price of this, however, is extra bulk, weight, and cost.
For hunting scopes, the most popular size is probably still the old favorite of 40, but you can certainly buy them in sizes of between 32 and 50. Realistically, unless you are doing something very niche, 50 is about as high as you want to go. After that, the performance gains are not likely to be high enough to justify the extra weight (and cost).
The exit pupil is actually a part of the objective lens, but it’s important enough to be worth a mention on its own.
Technically, the exit pupil is the diameter of the beam of light emitted by the scope. It is calculated by dividing the diameter of the objective lens by the power. In the example above, the “3.5-10×50” scope will have an exit pupil of between (50/3.5) 15mm and (50/10) 5mm depending on what power is being used. The “4×32” scope will have an exit pupil of exactly 8mm.
As a point of comparison, the pupil in the human eye generally has a range of 2mm to 8mm. The higher end of this range, however, will only apply once your eyes have become accustomed to lower-light conditions.
It is hugely important to understand that there is an inverse relationship between the power and the size of the exit pupil. In other words, as the power increases so the size of the exit pupil decreases. In even blunter words, the more you magnify, the less light your scope will be able to capture.
This means that you want to be careful about falling in love with modern scopes that offer super-high levels of magnification. They may be excellent for some niche applications but for most people, frankly, they’re a total waste of money which will make your shooting worse instead of better.
Experienced hunters will tend to stick with the old-favorite of a 3-9 (x40) power scope, some now go for 2-10. What’s more, most of the time, your scope will be on the lowest power setting because most of your shots will be at close range. The ability to go up to 9 or even 10 will, however, give you a bit of extra flexibility for long-range shots.
If you absolutely must have a scope with super-high magnification, then spend the money on one which starts at two or three and then goes up as high as you want. If you use a scope that starts high and goes higher, even if it doesn’t really look that way (say a five or a six), then you will routinely find yourself in situations where you can’t aim properly because you can’t see enough of the target. Think of it as being able to see a leaf in great detail but having no clue about where to find the relevant tree.
For completeness, higher magnification scopes can be useful for pest control. Basically, if you need to shoot really small critters, then you might need a bit more power. That said, even here, think about the realities of your situation. In other words, just because you can go out and spend money on a 6-24 scope, it doesn’t mean that you necessarily should if 6-12 will do the job just fine.
Remember, the more you magnify, the less light will get in through the exit pupil. This means that, after a certain point, all that magnification will become useless because you literally won’t be able to see!
To round out this section, we’ll finish by saying that power of one and two is only likely to be of real-world use if you’re planning on hunting dangerous game, or big game under 200 yards.
If this is your plan, you might want to go for a 1-4 scope which will not only allow you to take slightly longer shots but also function reasonably well for standard hunting. As previously mentioned, most of the time you’ll have your scope on the lowest power setting anyway.
One last point is that larger exit pupils are more forgiving of your head position. By contrast, the more you start pushing up the power and reducing the size of your exit pupil, the more important it becomes to have your head in exactly the right place.
The purpose of the reticle is to help the shooter aim correctly. It can be placed either in front of or behind the magnification lens. If it’s in front, then it’s described as a first focal plane (FFP) scope and if it’s behind, it’s described as a second focal plane (SFP) scope.
With a first focal plane scope, the size of the reticle changes as the size of the sight picture changes. With a second focal plane scope, the reticle stays the same.
Traditionally SFP scopes have been the staple hunting scopes because they are clearly visible regardless of the level of magnification. These days, however, some hunters are starting to prefer FFP scopes because they can make it easier to land accurate shots.
As is often the case in shooting, as in life, there is no “right and wrong” or “one-size-fits-all” solution. The best option is generally to try both and see which one you prefer.
You could also look at the new “hybrid reticles”, which put the focal point in the SFP so it stays the same size and everything else in the FFP so it changes size with the image. The only downside to these new hybrid reticles is that, currently, they only work with scopes that have an electronically illuminated aiming point (a red dot to help you aim).
The style of reticle you choose is also, largely, a matter of taste (and what works best for your preferred style of shooting). The “classic” reticle is simply two fine lines at right angles to each other, which cross in the exact middle, hence the fact that the reticle is commonly known as the cross-hairs.
In actual fact, however, the “classic” reticle has been falling out of favor since 1960 when Leupold came up with the Duplex reticle. This has thick, heavy, lines coming in from the outer edge, which then taper to the classic fine lines. The idea is that this naturally draws the shooter’s eye towards the center of the scope.
The Duplex reticle, or a variation thereof, is currently the staple reticle, however, these days scope technology is getting better and better at an impressive pace and bullet drop compensating technology (or more accurately ballistic drop compensating technology) is now starting to catch on.
BDC technology essentially means that your reticle will try to help you to compensate for the effect of gravity on your bullet. In principle, this is a great idea. In practice, as it currently stands, the implementation is so complex that it’s probably only of interest to the most dedicated and experienced of shooters. In other words, it’s definitely not (yet), the beginner-friendly option it might appear.
To begin with, you need some way of estimating range, which effectively means that you need to be comfortable using a laser range finder. If you’re using a first focal plane scope then you can generally use it at any magnification, but if you’re using a second focal plane scope, then you’ll generally need to set it at a specific magnification.
What’s more, there are all kinds of additional factors that could influence the accuracy of BDC technology. These include your choice of ammunition, your barrel, the elevation, the humidity, and the temperature.
In short, BDC may well turn out to be one of the most exciting developments since the invention of the scope (or the rifle), but it probably has some way to go before it becomes the new standard.
As a final point, it is increasingly common for manufacturers to include “electronically illuminated aiming points” (red dots for targeting) with their reticles. Many shooters find these very handy for sighting, especially at speed. Just remember, however, that these depend on LED lights which are battery-operated. This means that they only work for as long as the battery does.
The fact that LEDs use minimal power means that, in theory, a battery should last for ages. In practice, however, much will depend on how well you take care of your battery and the ambient temperature during use.
Batteries do not like extremes of temperature. If it’s extremely cold, their capacity will plummet (although they may recover when warmed up). If it’s extremely hot they may explode (although this is very rare). Sometimes, they will just expire for no apparent logical reason.
This means firstly, that it’s a really good idea to carry a spare battery with you (and to know how to change the battery) and secondly that it’s a really good idea to make sure that you can use your reticle without the LED as well as with it.
Rifle Scope Jargon Explained
Here’s a guide to some of the key terms used when describing (and selling) scopes – and what they actually mean in practice.
A lot of the time, the description of a scope will start with something like this – “3.5-10×50”. This translates as minimum power – maximum power x objective diameter. You may also see something like this “4×32”. This means that there is only one power setting. These days, most scopes have a range of settings to allow for more flexibility and convenience.
Power simply means how much the scope magnifies the field of view as compared to the naked eye. So, in the first example, the scope has a flexible power with a magnification factor from 3.5 to 10. In the second example, it has a fixed power with a magnification factor of 4.
In simple terms, you can think of the power as being like the lens on a camera. A zoom lens allows you to adjust the focus from low magnification (wide-angle shots) to high magnification (telescopic shots). This is particularly useful for hunters who want to scan an area for a target and then focus on it.
Fixed power lenses, however, may be a good choice for people who don’t really need flexibility and would be happy to look at a lower-cost option, for example, a pre-loved scope.
For completeness, as with camera lenses, the numbers on their own do not tell anything like the whole story. You want a good-quality lens from a reputable manufacturer.
Field of View
Technically the field of view (FOV) is the width of the area you can measure at a specific distance. In the U.S. the FOV is usually quoted in feet at a distance of 100 yards. If, however, you happen to be shopping internationally, be aware that the reference points may be different (for example centimeters and meters), although the basic idea will be the same.
There is a direct link between FOV and power. Low power means low magnification and hence a wide FOV, and high power means high magnification and hence a narrow FOV.
Despite what some adverts may imply, rifle scopes do not gather light. They simply transmit the available light through the various lenses and, at present, there is always some light lost along the way. Currently, most scopes will transmit around 90% of the light. The best (read most expensive) scopes can transmit up to 98% of the light.
Cynical as this may sound, it’s probably best not to put too much faith into the manufacturer’s stated figures for light transmission. Each manufacturer will have their own way of measuring it and the approach they use to doing so may not tally with the average person’s real-world experience. The size of the exit pupil is generally a more reliable guide.
For completeness, although the ability to make better use of the available light is possibly one of the biggest arguments in favor of using a scope (even when you could, in principle, have made the shot with the naked eye), as is generally the case in life, you want everything in moderation.
In other words, if the exit pupil on your rifle scope is significantly bigger than the pupil in your eye, then most of the light will be wasted because your eye literally won’t be able to process it.
Choosing a Scope For Your Rifle
The key to choosing the right scope for your rifle is to work out the minimum specification of scope you need for your intended use and then buy the best scope you can afford which meets those criteria.
Using this strategy means that you’ll avoid paying for features that, at best, you’ll not use (or at least not use enough to justify the bulk, weight, and cost) and instead put as much money as possible towards the lenses.
Taking Care of Your Scope
If you’ve spent good money on the best scope you can afford, then it makes sense to spend some time (and a little extra money) taking good care of it. Here are some tips.
The number one cause of damage to scopes is rough handling so be gentle. Ideally, when you are not using your rifle, you should take off the scope and put it in a protective case.
You should definitely take off your scope when you are cleaning your rifle. If, however, this is too much effort, at least put the flip covers on. This will protect your lenses from the fine mist which generally comes out of the bore when you pull out the cleaning brush. If you forget this, then remember to use a microfiber cloth to clean it off. Also, work gently. Your gun may stand up to rough handling but your scope won’t like it one little bit.
After each use (as in before you pack away for the day, not after each shot), hold your scope vertically and blow around the bottom end (with your mouth not any kind of air sprayer). Then flip it and repeat the exercise. This will do a lot to get rid of fine dust you might not notice.
Once a week or so, get a proper lens-cleaning brush (as in the sort you can use on a camera) and dust from the center outwards. Then use a microfiber cloth to clean off any smudges. If you’re struggling to get the cloth into the right places, wrap it around a cotton swab.
Make sure that your brush and microfiber cloth are clean, dry, and dust-free and resist the temptation to use water or any chemicals, especially solvents. Never, ever, under any circumstances whatsoever use any sort of regular glass cleaner on your scope!
With the lenses clean, you can move on to the body. Honestly, for the most part, giving the body a clean is purely for appearances so you could skip most of it if you really wanted. The bit that does matter is the adjustment knobs. You want to avoid getting any dirt in them.
To clean the body, use a different brush and just brush down it, paying particular attention to the knobs. When cleaning the knobs, brush away from the center. Basically, you want to brush the dirt away, not push it in. Smudges on the turrets don’t matter, but if you really want to get rid of them, use a different microfiber cloth. Again, make sure the brush and cloth are both clean and dry and resist the temptation to use any water or chemicals unless you are truly desperate.
If you have an LED light on your scope, now is a good time to check the battery port for rust. If you find any, you may be able to deal with it by cleaning the port gently with a regular pencil eraser. Go carefully, so you avoid damaging the leads.
Hi, I am Barry. I co-founded inteliscopes.com, so you get all the proper advice you need with such a vitally important purchase. With my love of guns and teaching people, I needed to share my knowledge with the world.